The invention relates to a combustion apparatus for a gas turbine engine. More particularly the invention relates to a wall structure for such a combustion apparatus.
A typical gas turbine engine combustor includes a generally annular chamber having a plurality of fuel injectors at an upstream head end. Combustion air is provided through the head and in addition through primary and intermediate mixing ports provided in the combustor walls, downstream of the fuel injectors.
In order to improve the thrust and fuel consumption of gas turbine engines, i.e. the thermal efficiency, it is necessary to use high compressor pressures and combustion temperatures. Higher compressor pressures give rise to higher compressor outlet temperatures and higher pressures in the combustion chamber, which result in the combustor chamber experiencing much higher temperatures than are present in most conventional prior combustor designs.
There is therefore a need to provide effective cooling of the combustion chamber walls. Various cooling methods have been proposed including the provision of a doubled walled combustion chamber whereby cooling air is directed into a gap between spaced outer and inner walls, thus cooling the inner wall. This air is then exhausted into the combustion chamber through apertures in the inner wall. The inner wall may comprise a number of heat resistant tiles, such a construction being relatively simple and inexpensive.
Combustion chamber walls which comprise two or more layers are advantageous in that they only require a relatively small flow of air to achieve adequate cooling. However they are prone to some problems. These include the formation of hot spots in certain areas of the combustion chamber wall. Prior art proposals to alleviate this problem include the provision of raised lands or pedestals on the cold side of the wall tiles, these lands or pedestals serve to increase the surface area of the wall element thus increasing the cooling effect of the air flow between the combustor walls. Compressor delivery air is convected between pedestals on the xe2x80x98cold facexe2x80x99 of the tile and emerges as a film directed along the xe2x80x98hotxe2x80x99 surface of the following downstream tile.
The provision of such lands is also accompanied by inherent problems. For example localised overheating may occur behind obstructions such as mixing ports or adjacent to regions of near stochiometric combustion conditions (hot streaks). A particularly hot region has been recently identified on the combustor wall immediately downstream of the fuel injectors. There is no provision for enhanced heat removal, either locally to remove hot spots or to alleviate more general overheating towards the downstream end of the tile. Overheating may occur downstream of the mixing ports since the protective wall cooling film is stripped away by the transverse mixing jets. Where design requirements have dictated a relatively long tile the cooling film quality towards the downstream edge of the tile may be poor and may lead to local overheating.
To alleviate the above problems, it is known to provide a low conductivity thermal barrier coating on the hot side of the tiles and/or to provide effusion holes within the tiles, to effect localised cooling. Such effusion holes are preferably angled, as this provides an increased cooling surface, and helps to lay down a cooling film on the hot side of the tile. The effusion holes are typically formed by laser drilling.
According to the invention there is provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure, the wall element including inner and outer walls defining a space therebetween, the wall element being of cast construction and including a plurality of cooling apertures provided therethrough and formed during the casting process.
Preferably the wall structure is for a combustor arranged to have a general direction of fluid flow therethrough, and the apertures lie in use at an angle of between 10xc2x0 and 40xc2x0 to that general direction of fluid flow.
Preferably the element includes a plurality of projections, which in use extend into the space between the inner and outer walls. An axis of at least one cooling aperture may lie on a line, which intersects at least one of the projections.
Preferably the wall element comprises a thickened portion, the thickened portion includes the plurality of cooling apertures.
Preferably the thickened portion defines a crescent shape.
The wall element may include one or more generally cylindrical projecting studs, the studs are provided for use in fixing the wall element to the outer wall of the wall structure, and at least one cooling aperture provided in or near a base region of a stud.
Alternatively or additionally, the wall element may include at least one integrally formed boss for a mixing port, and at least one cooling aperture provided in or near a base region of the boss.
A base region of a stud or of a mixing port boss may be extended to provide an integral land in which a cooling aperture is located.
According to the invention, there is further provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls defining a space therebetween, the wall element including a plurality of projections, each projection in use extends into the space between the inner and outer walls and the plurality of cooling apertures extend through the wall element, wherein an axis of at least one aperture lies on a line which intersects at least one projection.
According to the invention, there is further provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls defining a space therebetween, the wall element including one or more generally cylindrical projecting studs, the studs are provided for use in fixing the wall element to an outer wall of the wall structure, wherein a base region of the stud is extended to provide an integral land in which a cooling aperture is located.
According to the invention, there is further provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls defining a space therebetween, the wall element including at least one integrally formed boss for a mixing port, wherein a base region of the mixing port boss is extended to provide an integral land in which a cooling aperture is located.
The cooling aperture may be laser drilled.
According to the invention, there is also provided a wall structure for a combustor, the wall structure including inner and outer walls defining a space therebetween and the inner wall including a number of wall elements, one or more of the wall elements being as defined in any of the preceding paragraphs.
According to the invention, there is also provided a gas turbine engine combustion chamber including a wall structure as defined in the preceding paragraph.
According to the invention there is also provided a method of manufacturing a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls defining a space therebetween, wherein the method includes the step of casting a plurality of cooling apertures in the wall element.
The method may include the step of investment casting the wall element. The method may include the steps of providing one or more sprues within a working pattern of the wall element to be cast, and subsequently dissolving the sprues out of the cast wall element, thus forming the cooling apertures.